L31 Vortec 5.7 no-start problem

This is a discussion on L31 Vortec 5.7 no-start problem within the Technical / Maintenance forums, part of the General Discussion category; Hey all. I'm frustrated and running out of ideas, hoping you guys can give me some fresh ones! I've got ...

L31 Vortec 5.7 no-start problem

Hey all. I'm frustrated and running out of ideas, hoping you guys can give me some fresh ones! I've got a '99 L31 vortec 5.7 in my truck, sequential central injection (spider injector). I parked it about a week ago, and a few days later it wouldn't start. It cranks fine and sputters once in a while, but never starts.

My first thought was fuel. I put a gauge to it and it holds 57psi. Next I pulled a plug and watched the electrode while cranking... has a strong spark. The plug was very wet, so the injectors are spraying. I pulled the air intake duct, opened the throttle, and looked down into the upper intake. It's damp in there, but no puddling.

So I've got fuel, I've got spark, but still no start. I was thinking timing is off, but this system has a locked-down distributor. I pulled off the cap and the rotor is intact and still tightened down. So that would narrow a timing problem down to crank sensor, cam sensor, or computer... right? When cranking it, after I let go of the key it gives a little chug or pop, which to me seems like a timing issue. Are any of those parts common problems on this system? You guys think I'm on the right track with timing, or have any other ideas?

Re: L31 Vortec 5.7 no-start problem

57 is probably not enough FP. Those things tend to want at least 60, and usually more like 65, before they'll work reliably.

LEAVE THE TIMING ALONE!!!! It didn't just up and jump off into the ozone somehow all of its own accord for no reason. Just DIDN'T happen. Don't worry about it. Don't let that big nut that's supposed to stay between the driver's seat and the steering wheel, back off and fall under the hood and start banging around and monkeying with things. If you mess with it, then that's just ONE MORE thing you'll have to go back and fix once you identify the REAL problem, which that is NOT it.

A no-start is the easiest thing in all the world to troubleshoot. I'll take working on a no-start over a runs-like-crap any day of the week. There are 3 magic ingredients required for an engine to run: compression, spark at a reaonable time, and air/fuel in reasonable proportion and quantity. All you gotta do, is figure out which one disappeared, and put it back. Eh??

So, approach it logically, and realize that there's ONE thing somewhere that isn't right, and LEAVE EVERYTHING ELSE ALONE until you've found it. I'm reminded of a story my late little bro used to tell, from when he was the service write and asst mgr at a dealership. Car (Roadmonster w/LT1) comes in on a hook one day; was driving down the road, running fine, and just conked out. He assigns it to his "problem" tech because that's all he had left. Tech comes back and says it needs plugs, wires, Optispark, fuel system cleanout, fuel filter, and some other stuff. Little bro asks him "why did it stop running". Tech says he doesn't know but after he changes all that stuff it'll probably work and then he'll be able to rule all that out. Little bro asks him "one more time, why did it stop running". Tech tells him to go sell the customer what he says it needs and let him make some money from doing all that work. Little bro fired him ON THE SPOT.

Don't be that tech. In the case of the car above, ONE THING somewhere, up and broke. This lazy tech was going to empty the poor owner's wallet on futility, and either hope that it accidentally started wrking again, or that he could continue to screw the owner out of even more money on even more "maybe it's this, maybe it's that" uselessness. Don't be that tech.

Realize that some ONE THING failed, and all you have to do is find it. Think carefully what the ONE THING could be; it HAS TO BE something common to all 8 cyls, something that can easily fail (no space-alien visitations required, or multiple cascading chains of wildly improbable events, or stuff like that: ONE SIMPLE THING somewhere). Remember, when troubleshooting, keep it simple. "The simplest explanation that fits all the facts is usually the right one". Think carefully about that quote, one word at a time: simple, fits, all facts, usually, right. For example, the space aliens did not take a break from creating crop circles in Indonesia (their latest joke the last month or so) and come jack with your timing. That doesn't pas the "simple" test.

Now: we can be reasonably sure the compression didn't just go away while the truck was sitting. I think we can safely rule that out.

Likewise, if you've got nice big fat purplish-white sparks that look like they'll jump a ¼" gap, then that's good too. Not little wimpy yellowish-blue ones that look like your lawn mower's sparks, I mean BIG FAT ones. Check that, make sure. If the spark is weak it might need a dist cap or rotor or something. ONE THING. Not, every piece of the ignition system; not, move the timing, which if the bolt is tight, didn't move. Simple. Keep it simple.

Just because a plug is "wet", doesn't necessarily mean you have ENOUGH fuel. Your highest probabilty thing to have up and failed, involves fuel. All you have to do to identify that or rule it out, is pour some fuel into the intake. Gasoline or starting fluid will work for this test. I would put the truck back together; put the plugs back in and all that; and do this test FIRST. Just pour in an ounce or 2 and turn the key. Either it will start right up, or it won't. I'm betting it will fire RIGHT UP, and will then die. This indicates a fuel problem.

Re: L31 Vortec 5.7 no-start problem

Have you ever replaced the "spider" for the fuel injection? I was having problems similar to yours on my truck (rough starts, sputtering and eventually no start). Took the spider out and 4 of the 8 injectors were not firing.

Re: L31 Vortec 5.7 no-start problem

RBO4Av I appreciate the story about the parts changer, but that's not me. I did not say anything about changing my timing, and I'm well aware that aliens didn't come change it. The distributor is locked in and can't be turned, the timing is not adjustable. And if for some reason I decided to mess with the timing by pulling the distributor, I could easily put it back in correctly... done it a time or two before. The computer controls the timing using inputs from the crank and cam sensors. I actually read a TSB about crank position sensors going bad on these, causing the same issues I'm having. When it goes bad, the computer advances the timing 50 degrees while cranking. This is what I suspect to be the problem. I really do appreciate your help, but to be honest, the condescending tone of the post and the sarcasm are a bit offensive.
I'm aware of the clogging issues that this fuel system has. When I did this motor swap (it's in an s10) a few thousand miles ago, I hooked it up to an injector cleaner and flushed it. Prior to this no-start, the truck had no miss/hesitation/stumbling issues, so I don't believe it's the injection.

Re: L31 Vortec 5.7 no-start problem

Well I was wrong I guess... I apologize for that. It wasn't a fuel problem. However it also wasn't "timing", in the sense that, it wasn't that you HAD spark,just not aligned with the motor's internal motion; it was a NO SPARK problem. Very different from a "timing" problem.

The point I was trying to make was, DON'T twiddle the dist, or for that matter "adjust" anything, to try to fix it. All that does, is give you something you then have to UNdo once you find the REAL problem. Instead, attack the issue of finding WHAT BROKE. Which in this case, certainly would have been true: had you messed with the adjustment, then whenever you found the REAL problem (bad CPS) you would have had to go back and UN mess up what you had messed up by twiddling the dist.

But in any case, glad you got it fixed, and that it was something easy!

Re: L31 Vortec 5.7 no-start problem

Thanks man, it was a real relief when it fired up. It was a timing problem, though. It had spark, but when the CPS goes bad the computer for some reason advances the timing by 50 degrees during cranking, causing a no start problem... and sometimes breaking the starter! So yes, it was getting spark (which is what confused me to begin with!), but it was timed way off. Anyway, problem solved and will hopefully save someone some frustration.

Re: L31 Vortec 5.7 no-start problem

Originally Posted by Pauly

If you have a bad Crankshaft Position Sensor, you will have a no spark condition. The coil will not fire.

peace
PAuly

There were some issues with CKP's having a fault that caused the timing that the poster described. I remember reading the TSB but I don't know if GM said the fault was the affect of age, or possible rust like the low speed ABS that some vehicles experience

Re: L31 Vortec 5.7 no-start problem

Originally Posted by JeremyB

There were some issues with CKP's having a fault that caused the timing that the poster described. I remember reading the TSB but I don't know if GM said the fault was the affect of age, or possible rust like the low speed ABS that some vehicles experience

I do know that these systems are very picky when it comes to clearance between the reluctor wheel and the sensor. It would make sense that corrosion taking increasing or decreasing the clearance could cause an issue.
So many people throw new CKP sensors at no starts, its easy to rule out the fuel system. A shot glass of gas down the throttle body rules out lack of fuel. If it fires, you know its fuel.